1. Field of the Invention
The invention relates to a method and apparatus for obtaining a sharpness control, and to a display apparatus comprising such a sharpness control.
2. Description of the Related Art
In conventional luminance transient improvement circuits, a minimum and a maximum value of an input sample, and a plurality of delayed input samples are obtained. A selection circuit determines whether a center delayed input sample, the minimum value or the maximum value is to be outputted. The selection circuit obtains a 2nd derivative of the input signal. If the 2nd derivative is clearly negative, the minimum value is output, while if the 2nd derivative is clearly positive, the maximum value is outputted. If the 2nd derivative is around zero, the center delayed input sample is outputted. However, the perception of the resulting step signal on a TV screen with various scenes has the disadvantage that fine scene details, like hair, grass, leaves, etc., become very unnatural. It looks like whether fine details of a photo have been cut and pasted, resulting in clearly visible artifacts at the cut and pasted transients.
In conventional peaking circuitry with Laplacian filters, used in television receivers and video cameras, overshoots and undershoots will occur at rather steep steps. The perception of such exaggerated "ears" is in contradiction to the idea to reproduce a sharper picture.